One type of hybrid electric vehicle (HEV), commonly referred to as a mild hybrid vehicle or mild HEV, includes an engine and a belt-driven starter generator (BSG) unit. The BSG unit includes a battery system (e.g., 48 volts) that supplies a current to drive an electric motor, which in turn drives a crankshaft of the engine via a belt to assist in starting or restarting the engine. This enables the engine, for example, to be periodically turned off during certain operating periods and then quickly restarted when drive torque is required. This is also commonly referred to as engine start/stop engine operation. Such operation provides for increased fuel economy. The BSG unit is also configured to convert torque generated by the engine at the crankshaft to electrical energy for powering or recharging components, such as the battery system of the BSG unit.
A DC-DC converter is optionally implemented to step-down the voltage of the battery system to a lesser voltage (e.g., 12 volts) for recharging another battery (e.g., a lead-acid battery) that powers vehicle accessory loads and/or for directly powering the vehicle accessory loads. When a main contactor of the battery system opened due to a fault condition, the DC-DC converter requires an input voltage to continue operation of the vehicle. Conventional mild hybrid vehicle control systems implement additional power modules (e.g., capacitors) to provide this input voltage during main contactor faults. Such modules, however, are very expensive. Accordingly, while such mild hybrid vehicle control systems work for their intended purpose, there remains a need for improvement in the relevant art.